1) Field of the Invention
The present invention relates to a communication path setting apparatus, a communication path setting method, and a communication path setting program that set a communication path between at least a communication terminal device and a plurality of second networks connected through a first network, or more particularly to a communication path setting apparatus, a communication path setting method, and a communication path setting program capable of setting an appropriate communication path easily without a routing protocol or a path setting process on the part of the user.
2) Description of the Related Art
A communication path setting apparatus that sets a communication path between a communication terminal device and a plurality of second networks through a first network is generally known. In this communication path setting apparatus, a routing protocol is executed with a destination network according to a predetermined rule or the user sets a path for the communication path setting apparatus and determines a path according to the set path.
Japanese Patent Application Laid-Open (JP-A) No. 2003-152781, for example, discloses a conventional technique about a communication path setting apparatus in which the user sets the optimum path by correcting a routing table based on the attribute information and the connection information of the network in advance. JP-A No. 2003-115861, on the other hand, discloses a conventional technique about a communication path setting apparatus in which the user makes an inquiry at a name resolution server based on a routing table assigning the order of priority and thus sets a path by using name resolution.
In these conventional techniques, the communication path setting apparatus, upon receipt of a name resolution request of a destination host existing in a second network from a communication terminal device connected to a first network, transmits the particular name resolution request to the DNS (domain name system) server of the second network having the destination host, and in response to the name resolution request, receives a name resolution response containing the address information of the destination host retrieved by the DNS server. The IP address of the destination host contained in the name resolution response received is set in the routing table data, and transmitted to the communication terminal device that has issued the name resolution request. The communication terminal device that has received this IP address connects to the destination host according to the IP address thus received.
The conventional technique described above, however, poses the following problems. Specifically, according to JP-A No. 2003-152781, the routing table can be corrected based on the attribute information and the connection information of the network and thus can set the optimum path. Nevertheless, a unique service of notifying the attribute information and the connection information to the communication path setting apparatus is required, thereby limiting the destination. Another problem of this conventional technique is that the routing table is required to be set by the user in advance, and therefore the job of setting of a routing table is bothersome.
JP-A No. 2003-115861, on the other hand, harbors the problem that although the path can be set by the name resolution by making an inquiry at the name resolution server based on the routing table, the order of making an inquiry about the name is required to be set by the user in advance and therefore the setting of the order of priority is bothersome. Especially in the subscription line of an ordinary home, the routing protocol is rarely used and therefore the fact that the setting of the routing table and the order of priority is complicated is a great problem. Further, according to this conventional technique, the path to be set is addressed to a single device. In the case of communication with a multiplicity of devices, therefore, the routing table data are vast and complicated. As a result, the retrieval of the address in the packet transfer process consumes a considerable time. Especially in the subscription line of an ordinary home where the routing protocol is rarely used as described above, a path with an address in an appropriate network range cannot be set automatically.